Role of recombination, dissociation, and competition between exciton-charge reactions in magnetoconductance of polymeric semiconductor device

Magnetoelectrical measurements were performed on a diode structure, based on an anthracenecontaining poly(arylene-ethynylylene)-alt-poly(arylene-vinylene) denoted AnE-PVstat, to clarify the role of the recombination and dissociation of electron-hole (e-h) pairs in the magnetoconductance(MC). We report the observed MC under a weak magnetic field (<1 T) at room and low temperatures. Positive MC is observed and reaches up to 2% at a magnetic field of 450mT at room temperature. It is found that with the increase of the voltage, the MC effect decreases. We also report the difference in MC between perpendicular (Theta = 90°) and parallel (Theta = 0°) alignment of magnetic field with respect to the current direction. The experimental data were analyzed in the context of the e-h pair model, based on the Stochastic Liouville Equation. To interpret the experimental results on magnetoconductance measurements, anisotropic hyperfine interaction has been introduced through an anisotropic hyperfine field. The dissociation rates qS and qT of the singlet and triplet e-h pairs were determined from the best fit with experimental curves and are about 10^5 s^(-1), while the recombination rates of the singlet and triplet e-h pairs are kS~10^9 s^(-1) and kT~10^5 s^(-1), respectively. At low temperatures (T<60 K), an unexpected 'sign-reversal phenomenon' of the magnetoconductance is observed.